The performing of assays can involve the application of one or several fluids, such as wash buffers, reagents, and diluents, to a sample. Many assay steps are temperature dependent, as measurements may change based on the temperature of the assay reaction mixtures through the time course of the assay. Assay precision thus depends on a consistent temperature profile for each instance of the assay. Many assays also determine results by comparing measurements from different instances of an assay where some of the instances include measurement of known concentration calibrators. As a result, assay accuracy may also depend on a consistent temperature profile for each instance of the assay. Consistent temperature profiles for each instance of the assay help ensure precise and accurate assay results. In some assays, it may be desirable to maintain a constant temperature. However, the temperature of the sample, of the fluids, of the equipment performing the assay, or of the room in which the assay is performed can affect the assay reaction temperature, and change the temperature profile for different instances of an assay.
Maintaining the temperature of the assay reaction mixture within a desired range and/or at a desired temperature can be difficult as the volume of fluid applied to the sample may vary between steps and the steps of different assays performed on the same equipment may differ. The different types of fluids can be stored at different temperatures. Reagents may be stored at chilled temperatures in a refrigerated compartment, while wash buffers may be stored at room temperature. Thus, when the equipment performing the assay has to dispense reagents, wash buffers, or both, it can be beneficially able to dispense these fluids at temperatures that do not affect the assay reaction temperature. If an assay requires an assay reaction mixture temperature of approximately 37° C., then the chilled reagents and the room temperature wash buffers may be heated up to, and dispensed at, approximately 37° C.
Fluid may need to be rapidly dispensed to a series of assays, or alternatively, there may be extended periods of time between assays. In a high throughput assay system that processes hundreds of assays per hour, the fluid may need to be dispensed every few seconds to a series of assays. Alternatively, within the same assay, wash buffer fluid may need to be dispensed and aspirated every few seconds to the same sample in a multi-step wash sequence. When there are extended periods of time between assays, and thus between applications of a fluid to a sample, the temperature of the fluid may vary from the desired temperature and/or temperature range and/or can approach the ambient temperature of the room in which the assay is being performed. When a conventional dispenser is idle for an extended period of time, the probe and the pre-heated fluid contained in the probe can cool to and remain at the ambient temperature. For example, when a conventional dispenser is idle for approximately seven minutes, then the fluid contained in the probe, which was pre-heated to approximately 37° C., can cool to and remain at an ambient temperature of approximately 18° C. Thus, the pre-heated fluid contained in the probe has lost most of its heat energy to its surrounding environment.
Several techniques have been used to maintain a desired temperature and/or temperature range of the fluid. These include maintaining the ambient temperature of the room in which the assay is performed at the desired temperature and/or within the desired temperature range and/or heating the fluid via, for example, one or several tube heaters. While the fluid has been heated, previous designs have been unable to maintain the desired temperature of the fluid throughout the dispenser, including at the point of dispense, and over extended periods of time. These problems have been addressed by “back-drawing” fluid into heated portions of the dispenser and/or purging some of the fluid from the dispenser.
While the currently used techniques for maintaining the fluid at the desired temperature can be effective, they also have several disadvantages. Specifically, the maintenance of the ambient temperature of the room at the desired temperature and/or within the desired temperature range can be difficult and expensive, “back-drawing” the fluid can decrease the accuracy of the dispensed fluid volume by precipitating gases in the fluid column and throughput is decreased by the “back-drawing” and reheating of the fluid, and purging can decrease throughput and result in wasted fluid and costs associated therewith. Further, “back-drawing” and purging may require additional hardware, such as longer tubing or a reservoir for handling purged fluids, which would render a compact design difficult.